Compression fitting leaks from behind the nut

Hi ALL: I have read some of the posts but despite following the directions, I still find that my 1/2 inch compression fitting for a bathroom sink supply pipe (copper) is still leaking very slowly from behind the nut.
I did the following: + Cleaned the copper pipe with emory cloth + The pipe itself is new, so hopefully the roundness is not an issue (no visual flaw detected) + I inserted the nut, then the ferrule (out about 1/8th of an inch) and then tightened (not too much). + I donotice that I can physically slide the nut back and forth on the pipe (does it mean that I probably need to tighten it some more?)
What can I do to prevent this from leaking? The choices I have at this point are to call a professional plumber and have him solder the joint.
Would it help if I put teflon tape around the pipe and then inserted the nut and the ferrule on top of the pipe (thereby ensuring a snugger fit between the ferrule and the pipe)? I havent tried this approach though several folks have indicated that it works.
Thanks for any advice that you can provide,
Warm wishes Manju
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
ThinkNotes wrote:

After tightening, you should not be able to move the ferrule; it should have embedded itself right into the copper pipe. I wouldn't use tape, but you can apply a bit of sealant to the ferrule and then retighten.
Jim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks, Jim. I guess, I wasnt tightening enough, eh? What kind of sealant are you thinking about? I have JB Weld at home, in addition to the teflon paste (white stuff). Should I put the sealant to the tube so that the ferrule then slides on top and then gets sealed? Or should i just add some sealant to the outside-end of the ferrule where it meets the tube?
Best wishes/manju
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
ThinkNotes wrote: <SNIP>

Teflon paste/pipe dope would be good. It will make tightening easier also. Don't overtighten! As someone else suggested, WD-40 will also make it easier to tighten. It is a fine line between tight and too tight. <g> Jim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Soak the fitting iwth WD-40 adn retighten. Little tighter this time.
The WD helps the ferrule slip into the little spaces.
--
Christopher a. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Or you could learn to solder! The basics aren't very expensive and it is kinda fun.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.